Development of techniques for the effective use of solar heat has continued in recent years. Some of these techniques involve using a hot water feeder to heat water in a hot-water tank by solar heat recovered by a solar heat collector. The technique described in Japanese Utility Model Registration No. 3140747 is known as an example of such a hot water feeder.
The conventional hot water feeder is designed so that hot water heated by a solar heat collector is circulated by a pump and stored in a hot-water tank, and is provided with an incoming water pipe for feeding water to the hot-water tank from the outside, and a outgoing hot water pipe for delivering water from the hot-water tank to the outside. A feed water temperature sensor is mounted in the incoming water pipe, and an outgoing hot water temperature sensor and a flowmeter are mounted in the outgoing hot water pipe. A thermal energy meter calculates cumulative thermal energy on the basis of the temperature detected by the incoming water temperature sensor, the temperature detected by the outgoing hot water temperature sensor, and the flow rate measured by the flowmeter. Knowledge of the cumulative thermal energy allows the amount of substitute energy to be calculated.
To be used more widely, a hot water feeder must be designed with minimal costs. For this reason, it has been proposed to reduce the number of parts that do not directly contribute to the performance of the hot water feeder. A flowmeter is one such part that is relatively expensive. Costs are also involved in mounting the flowmeter in a pipe. On the other hand, it is preferable for the operator of a hot water feeder to have information about cumulative thermal energy.